Apparatus for simulating daylight and artifical light



Dec. 5, 1967 J. F. RENDINA I 3,355,982

APPARATUS FOR SIMULATING DAYLIGHT AND ARTIFICIAL LIGHT Filed Oct. 2,1963 2 Sheets-Sheet 1 FIG.!

MIDDLETON STANDARD DAYLIGHT STANDARD DAYLIGHT OF INVENTION '0 8 /7VIAVELENGTN-A INVENTOR JOHN F. RENIDINA ATTORNEY Dec. 5, 1967 J. F.RENDINA I 3 ,355,982

APPARATUSFOR SIMULNTING DAYLIGHT AND ARTIFICIAL LIGHT Filed Oct. 2, 19632 Sheets-Sheet 2 FIG. 3

ILLUNINANT A TUNG T EN LANP AT 2854 K INDOOR LIGHT OF INVENTIONINTENSITY FILTER FILTER 4 LANP'I LAMP2 LANP i Pmfi u 1Q 2o 52 5| FILTERFILTER IlS-IZO vous LAMP LWPHG 20 I by IN VENTOR JOHN F. R ENDINAATTORNEY United States Patent 3,355,982 APPARATUS FOR SIMULATINGDAYLIGHT AND ARTIFICIAL LIGHT John F. Rendina, Wilmington, Del, assignorto E. I. du

Pont de Nemours and Company, Wilmington, Del., a

corporation of Delaware Filed Oct. 2, 1963, Ser. No. 313,337 1 Claim.(CI. 88-44) ABSTRACT OF THE DISCLOSURE An apparatus for selectivelyconsecutively subjecting colored samples to a first condition simulatingnormal daylight and a second condition simulating indoor artificiallighting, the apparatus having two groups of light source units arrangedso that one group is used to produce both conditions with simpleswitching arrangement to add or subtract the other group, the unitsbeing arranged so that a single switch action not only adds or subtractsthe necessary light source units but controls the voltage necessary foroperating the light source units at the desired temperature level.

This invention relates generally to the field of matching colors. Morespecifically, it involves an improved apparatus for producing simulateddaylight and also simulated light representative of ordinary artificialindoor lighting for obtaining a visual color match or comparison ofdesired materials under the two conditions of lighting. This arrangementis of special interest and bonefit in handling materials which have beentreated with the so-called white dyes, or optical brighteners, toproduce a fluorescent effect. These white dyes, or optical brightenersabsorb light in the ultraviolet spectrum and fluoresce in the blue partof the spectrum to produce an actual emission of blue light from thedyed material which light is added to the light reflected from thematerial. The

reflected light, of course, is the light returning from the dyedmaterial after absorbtion of certain of the spectral components of theincident light by other component dyes present in the material. Thesewhite dyes, also known as whitening agents, are widely used to improvethe appearance of textile and paper. An important need exists withmanufacturers and consumers of such products for a suitable method fordetermining the color quality and relative whitening efliciency of thevarious fluorescent whiteners. This type of comparison is conventionallyaccomplished by visual examination. In general, no reliable device forqualitative visual examination, or comparison, of materials treated withthese whitening agents has been developed. Ordinarily, a comparison ofthis sort is made by directing light on samples of the dyed materialsfrom a light source having the same ultraviolet spectral energydistribution as daylight, and then viewing and comparing the reflectedand fluorescent light from the samples.

However, although commercial ultraviolet light sources are availablewhich will cause these dyed materials to fluoresce, in most of theseavailable sources the visible spectral component of light has beenfiltered out and removed by an enclosure or envelope surrounding thesource. This renders such light sources unsatisfactory as means forsimulating natural light. In addition, it has been established that itis generally necessary to check any color match, or comparison, underthe light from two difierent sources, one representing a standarddaylight spectral distribution, and the other representing some standardindoor or artificial lighting spectral distribution, so that the colorrelationship is maintained on der both indoor and outdoor lighting. Thisapproach is made necessary due to the fact that most materials exhibit aproperty known as metamerism which is the apparent change in color dueto a change in spectral distribution of the illumination applied.

It is an object of this invention to provide a single improved apparatusfor convenient and eflicient comparison of color samples under light ofa standard daylight spectral distribution and also under light of somestandard indoor or artificial spectral distribution.

It is another object to provide such an apparatus combination whichutilizes simplified and improved light sources for the production ofstandard daylight spectral distribution and for the production of thestandard indoor, or artificial, spectral distribution.

It is yet another object to provide in such a combination an improvedarrangement and simplified electrical circuitry for actuating the sameto produce the desired comparison.

Yet another object is the provision of such a color sample apparatus ordevice which is simple and economical to manufacture, operate, andmaintain; yet effective and reliable in its functioning.

These objects are accomplished in an apparatus which generally comprisesa supporting or housing structure defining a chamber for receiving colorsamples for comparison, said apparatus further comprising a lightingsystem for selectively sequentially subjecting samples in the chamber tolight having a first spectral distribution corresponding to ordinarydaylight and to light having a second spectral distribution representingor corresponding to the other lighting conditions to which the sampleswould be subjected, said lighting system comprising in combination afirst plurality of electrically actuated light source units which underfirst given voltage conditions produce the simulated daylight accordingto the Middleton spectral distribution, and a second plurality ofelectrically actuated light source units, which under second givenvoltage conditions and in cooperation with said first plurality of lightsource units, produce light having the second spectral distribution, andelectrical means operatively connected and cooperating wtih said lightsource units for selectively operating said units to produce said twotypes of light.

Other objects and advantages will appear from the following detaileddescription of the apparatus provided in accordance with the aboveobjects, and the appended claims, considered in conjunction with theaccompanying drawings in which:

FIGURE 1 is a graphical representation of wave length versus energy oflight representing average daylight spectral distribution as determinedby the Middleton skylight (W. E. Knowles Middleton of the NationalResearch Council of Canada) and of the light approximating thisMiddleton daylight as produced by the apparatus of the presentinvention.

FIGURE 2 is a partial vertical sectional view taken through theapparatus of FIGURE 5 to illustrate one of the light source units forproducing the standard daylight spectral distribution according toMiddleton.

FIGURE 3 is a graphical representation of wave length versus energy oflight representing the standard indoor artificial spectral distribution(Standard C.I.E. illuminant A-an unfiltered tungsten filament sourceoperating at 2854 K.) and of light approaching this standard indoorspectral distribution as produced by the apparatus of this invention.

FIGURE 4 is a schematic diagrammatic showing of the arrangement of lightsource units :and associated circuitry of the apparatus embodying thepresent invention.

FIGURE 5 is a perspective view of the apparatus of the present inventionshowing the light source units and location of color samples beingcompared or matched.

Since the measurements made by W. E. Knowles Mid- :lleton, NationalResearch Council of Canada, of the daylight spectral distributionextending over the ultraviolet and visible portion of the spectrum arebelieved to represent the most reliable and complete set of dataavailable to date, these measurements, as indicated generally in FIGURE1, have been adopted as a basis for light having the standard daylightspectral distribution used in the present invention. The dotted line inFIGURE 1 indicates the standard daylight spectral distribution of lightproduced by the apparatus of this invention. For the standard indoor,artificial lighting spectral distribution used in the apparatus of thisinvention, the standard C.I.E. illuminant A, which is represented by anunfiltered tungsten filament source operating at 2854 K., has beenadopted. The standard C.I.E. illuminant A distribution and that producedby the apparatus of this invention are indicated in FIGURE 3.

The improved apparatus provided in accordance with the above objects ofthe invention is illustrated in FIG- URES 2, 4 and 5 of the drawings andcomprises a housing formed by side wall elements 10, a bottom or baseelement 11 and a top member 13 which contains the light source units,and associated electrical means for actuating and controlling theseunits. The color samples S are shown in position for examination andcomparison.

There are two groups of light source units, a first group which aloneproduces light having the standard daylight spectral distribution; and asecond group which together with the'other group jointly produce thelight having the standard indoor or artificial light spectraldistribution. The light source units of the first group are designatedas lamps No. 1, No. 2, No. 3 and No. 4, one of which is shown in anenlarged view in FIGURE 2. Light source units of this first group eachcomprises a lamp provided with a tungsten filament 22 which is heated toincandescence and operated at 3100 K. by electric current throughconductors 28. The filament 22 is maintained in a sealed evacuatedquartz envelope 21 which also contains a small amount of iodine whichcombines with the tungsten that is deposited in the envelope 21 duringoperation to form a tungsten iodide vapor which subsequently breaks downinto the original iodine and original tungsten as it comes in contactwith the hot filament 22. Lamp 20 is used in combination with a filterelement which will pass the ultraviolet and blue portion of lightgenerated by the lamp but which will pass relatively smaller amounts ofyellow and red.

It has been found that a commercially available bulb of the type made bythe General Electric Company and identified by Catalog No.6.6A/T4Q/CIr-2OOW in combination with a filter of the type made by theCorning Company and identified as Corning glass filter l64, in athickness which is about 0.15 X to about 0.5x of stock thicknesscooperate to produce the Middleton standard daylight spectraldistribution as shown in FIGURE 1. These light source units of the firstgroup are positioned as shown in FIGURE 5 to give even application oflight over samples S positioned on the base element 11. The voltagerequired for each lamp 20 of the first group units to produce thestandard Middleton daylight spectral distribution (tungsten filament at3100 K.), is between 28.75 and 30 volts which can conveniently beachieved by connecting the four light producing units in series with a115-120 volt source as indicated in FIGURE 4 by closing switches 51 and52.

The light source units of the second group, which together with thefirst group units produce the indoor artificial light spectraldistribution, each comprise the same lamp units as used in the firstgroup units but without the filter elements. By adding two of theseunfiltered lamps in series with four of the lamps of the first groupunits to give a voltage for each lamp of from 18-20 volts (for instanceby opening switch 52 and maintaining switch 51 closed in the circuit ofFIGURE 4), a spectral distribution matching or corresponding to theC.I.E. illuminant A (standard indoor lighting; tungsten filament at 2854K.), is produced. Thus with this relatively uncomplicated structuralarrangement and electrical connections, and with simple switchactuation, two standard spectral distributions of light can be appliedto sets of material or color samples to give a comparison for matchingthe samples at each of two commonly encountered lighting conditions.Other lighting conditions to be encountered could also be duplicated byusing additional groups of suitably different light producing units.

The operation of the apparatus in carrying out examination andcomparison of color samples is believed to be clear from the abovedescription.

The samples S are placed in suitable locations in the chamber defined bythe wall elements It), the top element 13 and bottom elements 11, and inthe desired sequence the lamps No. 1, No. 2, No. 3 and No. 4representing the first group light producing units for generating thestandard daylight or Middleton spectral distribution, are actuated byclosing switches 51 and 52, and then all the lamps No. 1, No. 2, No. 3,No. 4, No. 5 and No. 6 are actuated by closing switch 51 and openingswitch 52 to give the standard indoor lighting (C.I.E. illuminant A)spectral distribution. These steps can be accomplished in any desiredsequence.

This sequential examination and comparison of samples Will quickly andefiectively indicate whether or not a color match exists under each ofthe representative lighting conditions. The variation in the voltagedrop across the lamps 20 occurring with the change in circuit conditionsassociated with opening switch 52 while switch 51 is closed, issufficient to alter the characteristics of the first group of lightproducing elements such that in conjunction with the second group thesecond desired light conditions are produced directly. The loweredvoltage across each lamp produces a lower filament operating temperatureand in conjunction with the added number of unfiltered lamps producesthe C.I.E. illuminant A spectral distribution in a very simpleoperation.

It is believed to be clear that a novel, useful, and improved apparatusfor examination and comparison of color samples has been provided inaccordance with the objects of the invention.

Although a preferred embodiment of the invention has been described indetail in accordance with the patent statute, it will be obvious tothose skilled in the art that modifications may be made in thisapparatus without departing from the spirit of the invention and suchare considered to fall within the scope of the following claim.

I claim:

An improved simplified apparatus for examining samples of material todetermine their color under a first condition simulating normal daylightand under a second condition simulating indoor artificial lighting, saidapparatus comprising a housing structure, said housing structuredefining a chamber for receiving and supporting samples of material forexamination, said apparatus further comprising a lighting system forselectively sequentially subjecting samples positioned in said chamberto light having a first spectral distribution corresponding to ordinarydaylight and also to light having a second spectral distributionrepresenting artificial indoor lighting to which the material of thesamples would be subjected, said lighting system consisting solely of,in combination, a first plurality of identical electrically actuatedlight source units which under a first voltage condition produce in saidchamber the simulated daylight, a second plurality of electricallyactuated light source units, said units being identical with the unitsof said first plurality which under a second voltage condition, and incooperation with said first plurality of light source units, produce insaid chamber light representing artificial indoor lighting conditions,and electrical means adapted to be conected to a ll5-120 volt source ofelectrical voltage and operatively connected with said light sourceunits for selectively operating said units to produce alternately lightof said two spectral distributions, said units of said first pluralityeach consisting of a lamp having a tungsten filament sealed in anevacuated quartz envelope in combination with a filter which passes blueand ultraviolet light but limits a significant portion of red and yellowlight applied thereto, said units of said second plurality eachconsisting of an unfiltered lamp having a tungsten filament sealed in anevacuated quartz envelope, said electrical voltage source and electricalmeans being arranged to supply selectively a voltage directly solely tosaid units of said first group in series sufiicient to operate saidfilaments at 3100 K. which provides radiation corresponding to standarddaylight, or alternatively directly to the units of both groups inseries to operate said filaments at a significantly lower temperaturewhich provides radiation corresponding to standard (C.I.E. illuminant A)indoor lighting, said first plurality of units consisting of four lampsin series, each lamp having an operating voltage of from 28.75 to 30.0volts when supplied directly and solely by said source and said secondplurality of units consisting of two lamps each having an operatingvoltage of 18-20 volts when connected in series with each of said lampsof said first plurality across said voltage source, said electricalmeans comprising a switch device for alternately connecting either theunits of said first plurality in series across said source or all of theunits of both pluralities in series across said source, the units andswitch device arranged so that a single actuation of the switch devicealso directly and instantly controls the voltage as necessary to achievethe desired filament operating temperature level for the units in eachcondition.

References Cited UNITED STATES PATENTS 774,812 11/1904 Wurts 315122 X1,423,882 7/1922 Radford 240-1.1 1,442,166 1/ 1923 Macbeth 2401.11,608,685 11/1926 Vesser 8814 2,110,500 3/1938 Chiera 2401.1 2,831,1204/1958 Weeks 88-14 X 3,093,319 6/1963 Gamain 2401.1

JEWELL H. PEDERSEN, Primary Examiner. W. A. SKLAR, Assistant Examiner,

